Nutrient returns in excreta on grazed dairy soils

Year of study:

2012

Project ownership:

Department of Primary Industries

Future Farming Systems Research

Contact:

Sharon R Aarons– sharon.aarons@dpi.vic.gov.au

Cameron JP Gourley– cameron.gourley@dpi.vic.gov.au

Project details

Objectives:

Within grazed dairy systems better understanding of the spatial and temporal location of dairy cows can lead to a greater awareness of the potential for heterogeneous nutrient distribution and contribute to management practices that minimise nutrient accumulation. An approach was tested on ten dairy farms around Australia where the location of cows in space and time was documented. In conjunction with feed data, nutrient deposition in management units around the farms was estimated.

Hypotheses:

Nutrient recycling and deposition in dung and urine from grazing cows can contribute to the uneven distribution and accumulation of nutrients on dairy farms.

 

Basis of trial:

Dairy production systems are often in net positive nutrient balance (Gourley et al. 2012) with potential for losses of nutrients from farms to waterways and the atmosphere (Gourley and Ridley 2005, Monaghan et al. 2007). Nutrient losses are often associated with the accumulation of nutrients in parts of the landscape where transport pathways exist (Monaghan et al. 2007). Data from grazed dairy farms around Australia indicate considerable heterogeneity in nutrient concentration around farms (Gourley et al. 2010). Nutrient application in the form of fertiliser or effluent from dairy sheds and animal management practices such as night paddocks, strip-grazing and holding areas can lead to large amounts of nutrients deposited onto specific paddocks within a farm. In addition to farm management practices, animal behaviour can contribute to nutrient accumulation zones due to the propensity for dairy cows to congregate around water (waterways and troughs), under trees and on slopes

Location details

A subset of ten farms participating in the Accounting for Nutrient project was sampled (Gourley et al. 2010). The farms were located in Gippsland, the South West and the Northern regions of Victoria, New South Wales, Queensland and Western Australia, and represent different grazing management systems across Australia (Table 1).

Figure 1: Phosphorus (kg) deposited in dung around Farm 28 over 421 days by a) lactating dairy cows and by b) all cows (lactating, dry, heifers, springers).

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Summary of key findings of trial

Analysis of data indicated that cows spend a small proportion of their time in dairy sheds (2%) and yards (8%) where nutrients are likely to be collected for reuse, with similar time spent in feedpads (8%) and holding areas (2%). However, when analysed only for farms with feedpads, cows spent twice as much time in these locations. High nutrient accumulation can occur in these areas, and needs careful management to reduce its impact on nutrient losses. The largest amounts of nutrients (26, 5 and 39 t of N, P and K respectively) were recycled by cows to grazed paddocks, but these were not uniformly returned, with accumulations occurring in specific parts of the landscape.

Conclusion

The spatial and temporal movement of dairy cows appears to contribute to the heterogeneous distribution of soil nutrients observed on many dairy farms. Additionally, as the use of supplementary feeding increases, dairy cows are spending an increasing amount of time in areas where the nutrients they excrete are concentrated and not immediately available for recycling. The loss of nutrients from production, the potential for nutrient contamination from feedpads and holding areas, and the accumulation of nutrients in parts of the landscape are substantial factors that may hinder sustainable management of grazed dairy systems.

 

Table of results:

Table 1:

Percent time cows spent in different management units on ten commercial Australian dairy farms.

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Table 2:

Mean percent time spent by lactating dairy cows in management units on ten Australian dairy farms, on farms with feedpads and farms without feedpads.

Cows spent on average 2 and 8% of their time in the dairyshed and adjacent yards respectively, both of which are usually concreted and where excreted nutrients are likely to be collected for reuse.

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Where feedpads were present, dairy cows spent a mean of 15% of their time on them (Table 2), which would lead to the deposition of large amounts of nutrients in these areas. An estimated 19 and 3 kg nitrogen (N) and phosphorus (P) respectively would be deposited on a feedpad over a 300-day lactation by each cow in a dairy herd. However in only two of these farms were the feedpads concreted to assist with collection of excreta for reuse, suggesting that nutrients that could be recycled in these systems are potentially wasted. Providing supplementary feeding on feedpads or in holding areas has become more prevalent in Australian grazed dairy systems as a means of increasing milk production (Thorrold and Doyle 2007).

On all the dairy farms studied, the greatest proportion of time was spent on grazed pastures, even where feedpads or holding areas were used (Table 2). Based on dietary intake and milk production, the daily nutrients excreted by cows on Farm 28 were calculated (Table 3). Nitrogen, P and potassium (K) returned to pastures in a year were 26, 5 and 39 t respectively, while only 3, 0.6 and 4.5 t were deposited in the dairy shed and yards (Table 4). From an agronomic point of view these amounts are important when applied to the grazing area as a whole, amounting to 90 and 20 kg/ha/year N and P respectively. The N and P imported onto this farm in fertiliser over the year were 74 and 8 kg/ha respectively (data not presented).

Table 3:

Calculated nutrients excreted (g/cow/day) by lactating dairy cows from Farm 28, a commercial dairy farm in south west Victoria.

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Table 4:

Annual deposition of nutrients (t) by lactating dairy cows in management units around Farm 28.

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Measurements

On each of five visits (February, May, August and November 2008 and February 2009), farmers were asked to identify all locations on their farms that their lactating herds had visited in the previous 24 hours and the time the cows spent in each of these locations. Locations were grouped into the following management units: ‘Paddocks’, ‘Dairyshed’ (where cows are milked), ‘Yards’ (holding areas adjacent to the dairyshed), ‘Laneways’, ‘Feedpad’ (areas where cows are fed, which may or may not be concreted) and ‘Holding areas’ (other areas where cows are confined).

Samples of the diet offered to the lactating herds were collected as well as information about the amounts fed and any wastage. Feed samples were analysed for metabolisable energy and nutrient (crude protein, phosphorus, potassium, sulphur) content. Milk samples collected from the vats were analysed for nutrient, fat and protein content. Feed nutrients were calculated and then subtracted from the milk nutrients produced to estimate the nutrients excreted by the herd.

Reporting

How results have been reported:

Soil Science Australia 2012 Joint Australia and New Zealand Soils Conference p.461

References:

• Gourley CJP, Dougherty WJ, Weaver DM, Aarons SR, Awty IM, Gibson DM, Hannah MC, Smith AP, Peverill KI (2012) Farm-scale nitrogen, phosphorus, potassium and sulphur balances and use efficiencies on Australian dairy farm. Animal Production Science (published online 3 July 2012)

• Gourley CJP, Aarons SR, Hannah MC, Dougherty WJ (2010) Soil nutrient concentrations and variations on dairy farms in Australia. In Proceedings of the 19th World Congress of Soil Science. Soil Solutions for a Changing World. (World Congress of Soil Science. Brisbane).

• Monaghan RM, Hedley MJ, Di HJ, McDowell RW, Cameron KC, Ledgard SF (2007) Nutrient management in New Zealand pastures—recent developments and future issues. New Zealand Journal of Agricultural Research 50, 181-201.

• Gourley CJP, Ridley A (2005) Controlling non-point pollution in Australian agricultural systems. Pedosphere 15, 763-777.

• Thorrold BS, Doyle P (2007) The challenge for pasture-based dairying: learning from the unrecognised systems experts, good farmers. In Proceedings of the Australasian Dairy Science Symposium. Meeting the challenges for pasture-based dairying. (Ed DF Chapman et al.) pp. 450-460. (National Dairy Alliance. Melbourne).

Next steps

Recommendations

Improved nutrient management will depend on an understanding of the spatial and temporal patterns of animal movement and the implications for nutrient return and accumulation